Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit

[Eugenio Perez Martin]

On Wed, Jun 29, 2022 at 6:12 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
> On Fri, Jun 24, 2022 at 12:08 AM Eugenio Pérez <eperezma@xxxxxxxxxx> wrote:
> >
> > Userland knows if it can suspend the device or not by checking this feature
> > bit.
> >
> > It's only offered if the vdpa driver backend implements the suspend()
> > operation callback, and to offer it or userland to ack it if the backend
> > does not offer that callback is an error.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> > ---
> >  drivers/vhost/vdpa.c             | 16 +++++++++++++++-
> >  include/uapi/linux/vhost_types.h |  2 ++
> >  2 files changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 23dcbfdfa13b..3d636e192061 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> >         return 0;
> >  }
> >
> > +static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> > +{
> > +       struct vdpa_device *vdpa = v->vdpa;
> > +       const struct vdpa_config_ops *ops = vdpa->config;
> > +
> > +       return ops->suspend;
> > +}
> > +
> >  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> >  {
> >         struct vdpa_device *vdpa = v->vdpa;
> > @@ -577,7 +585,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >         if (cmd == VHOST_SET_BACKEND_FEATURES) {
> >                 if (copy_from_user(&features, featurep, sizeof(features)))
> >                         return -EFAULT;
> > -               if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> > +               if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> > +                                BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> > +                       return -EOPNOTSUPP;
> > +               if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> > +                    !vhost_vdpa_can_suspend(v))
>
> Do we need to advertise this to the management?
>

Not sure if I follow, the feature bit is not exposed if the backend
cannot suspend.

Thanks!

> Thanks
>
> >                         return -EOPNOTSUPP;
> >                 vhost_set_backend_features(&v->vdev, features);
> >                 return 0;
> > @@ -628,6 +640,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >                 break;
> >         case VHOST_GET_BACKEND_FEATURES:
> >                 features = VHOST_VDPA_BACKEND_FEATURES;
> > +               if (vhost_vdpa_can_suspend(v))
> > +                       features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> >                 if (copy_to_user(featurep, &features, sizeof(features)))
> >                         r = -EFAULT;
> >                 break;
> > diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> > index 634cee485abb..1bdd6e363f4c 100644
> > --- a/include/uapi/linux/vhost_types.h
> > +++ b/include/uapi/linux/vhost_types.h
> > @@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
> >   * message
> >   */
> >  #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> > +/* Device can be suspended */
> > +#define VHOST_BACKEND_F_SUSPEND  0x4
> >
> >  #endif
> > --
> > 2.31.1
> >
>